The later model Onan generators - when carefully installed by the manufacturer - are quiet and vibration-free enough both inside and outside the rig to actually be quite tolerable even for long run times.
We use the Onan in our 2005 Class C motorhome a lot and it's not irritating at all, so it is possible to have a decent built-in Onan experience. That being said, we do also carry along a small Honda generator - that is even quieter than the Onan - for very economical extended battery charging in ultra noise sensitive camping situations. The little Honda is also drycamping backup, should the Onan ever not start.